Land based unit for seismic data acquisition

ABSTRACT

A self-contained, wireless seismic data acquisition unit having a cylindrically shaped case with smooth side walls along the length of the case. A retaining ring around the circumference is used to secure the cylindrical upper portion of the case to the cylindrical lower portion of the case. Interleaved fingers on the upper portion of the case and the lower portion of the case prevent the upper portion and the lower portion from rotating relative to one another. Ruggedized external electrical contacts are physically decoupled from rigid attachment to the internal electrical components of the unit utilizing electrical pins that “float” relative to the external case and the internal circuit board on which the pins are carried. The seismic sensors in the unit, such as geophones, and the antennae for the unit are located along the major axis of the cylindrically shaped case to improve fidelity and timing functions.

CROSS-REFERENCES TO RELATED APPLICATIONS

This application claims the benefit of priority under 35 U.S.C. §121 asa divisional of U.S. patent application Ser. No. 14/108,199 filed onDec. 16, 2013 and titled “Land Based Unit for Seismic Data Acquisition”,which claims the benefit of priority under 35 U.S.C. §120 as acontinuation of U.S. patent application Ser. No. 12/154,413 filed on May22, 2008 and titled “Land Based Unit for Seismic Data Acquisition”, nowU.S. Pat. No. 8,611,191, each of which are incorporated by referenceherein in their entirety.

FIELD OF THE INVENTION

The present invention provides a land-based system for collectingseismic data by deploying multiple, autonomous, wireless, self-containedseismic recording units or pods. Seismic data previously recorded by thepod can be retrieved and the pod can be charged, tested,re-synchronized, and operation can be re-initiated without the need toopen the pod.

DESCRIPTION OF THE RELATED ART

Seismic data collection systems deployable on land are known in theprior art. Such systems typically comprise a plurality of distributedreceivers, i.e., geophones, connected in a parallel-series combinationon a single twisted pair of wires to form a single receiver group orchannel for a station. During the data collection process, the outputfrom each channel is digitized at the station and either stored ortransmitted back to a central location for subsequent analysis.Commonly, cable telemetry is used for data transmission between theindividual receivers, the stations and the central location. Othersystems use wireless methods for data transmission stations and are notconnected to each other. Still other systems temporarily store the dataat each station until the data is extracted.

SUMMARY OF THE INVENTION

The present invention provides a land-deployable system for collectingseismic data utilizing multiple, wireless, self-contained seismic datasensor units. Each individual seismic unit is self-contained such thatall of the electronics are disposed within the case, including one ormore geophones, a seismic data recording device, a power source and aclock. The electronics are housed in a sealed cylindrical package of ashape and having features which enhance manufacture, deployment andmaintenance.

More specifically, the cylindrical package includes a cylindricallyshaped container portion and a cylindrically shaped top portion. Thecontainer portion and top portion mate together to form a sealedenclosure in which the electronics are housed. The exterior of thecylindrical package is substantially smooth along its length.

In one embodiment of the invention, the top portion includes externallyaccessible electrical pads, which electrical pads are internally wiredto the electronics of the package. In such an embodiment, each portionincludes teeth which engage the teeth of the other portion when the twoportions are mated together. In this way, the cylindrical top portion isprevented from axially rotating or twisting relative to the cylindricalcontainer portion, thereby preventing potential damage to the internalwiring.

In another embodiment, an exterior groove is formed around the peripheryof the mated top and container portions, and a split ring is deployed inthe groove to fasten the two portions together, thereby avoiding theneed for other types of metal fasteners which can become difficult tomanipulate as they are worn or covered with debris, such as mud, fromdeployment. Typically, these other fasteners also require some type offlange, lip or other external projection which can inhibit deploymentand retrieval, as well as coupling of a unit with the earth. Moreover,because such fasteners are discreetly positioned on a unit, unequalforces may be placed on the unit as the fasteners thermally expand andcontract relative to the plastic the are mounted in. This can causenegatively impact the seal of such units.

In yet another embodiment of the invention, the external electricalconnectors are physically decoupled from rigid attachment to either theexternal case or the internal circuit board(s) of the unit, therebyavoiding stress on the circuit board from the varied expansion andcontraction of the components of the system, such as the plastic caseand the circuit board. The external electrical connectors include pinsthat “float” relative to the external case and the internal circuitboards.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is an exploded view of a seismic data unit package.

FIG. 2 is an exploded view of a seismic data unit package.

FIG. 3 is top view of the unit of FIG. 1.

FIG. 4 is a side view of a cross-section of the electrical connector pinsystem of the invention.

FIG. 5 is a upper orthogonal view of the pin of FIG. 4.

FIG. 6 is a lower orthogonal view of the pin of FIG. 4.

FIG. 7 is another embodiment of the pin of the electrical connector pinsystem of the invention.

DETAILED DESCRIPTION

In the detailed description of the invention, like numerals are employedto designate like parts throughout. Various items of equipment, such asfasteners, fittings, etc., may be omitted to simplify the description.However, those skilled in the art will realize that such conventionalequipment can be employed as desired.

With reference to FIGS. 1 and 2, there is shown a seismic datacollection unit or pod 10 of the invention. Pod 10 is comprised of acylindrical case 12 formed by a top cap section 14 and bottom containersection 16.

Cap section 14 is formed of a cylindrical wall 18 extending from a firstend 20 to a second end 22, which wall 18 is characterized by an outersurface 24 of a first diameter, an inner surface 26, a closed end 28 at22 and an opening 29 formed at first end 20.

Container section 16 is likewise formed of a cylindrical wall 30extending from a first end 32 to a second end 34, which wall 30 ischaracterized by an outer surface 36 of a first diameter, an innersurface 38 of a second diameter, a closed end 40 at 34 and an opening 42formed at first end 32.

Cap section 14 is provided with a plurality of teeth 44 extending aroundthe periphery of cap section 14 and container section 16 is providedwith a plurality of teeth 46 extending around the periphery of containersection 16. In one embodiment of the invention, the teeth 44 of the capsection 14 are spaced apart so as to form notches 48 therebetweendisposed to receive the teeth of 46 of container section 16 when capsection 14 and container section 16 are joined together. Likewise, theteeth 46 of the container section 16 are spaced apart so as to formnotches 50 therebetween disposed to receive the teeth of 44 of capsection 14 when cap section 14 and container section 16 are joinedtogether, such that the alternating teeth 44, 46 are interleaved withone another. When so joined, the meshed teeth prevent cylindrical capsection 14 from axially rotating or twisting relative to containersection 16. While the teeth and notches are depicted as rectangular inshape, those skilled in the art will appreciate that the teeth andnotches could have any shape so long as they join together to preventrelative rotation of the cap and container sections.

In one embodiment, an edge 52 is defined at first end 32 of containersection 16 and teeth 46 are disposed to extend axially from edge 52.Preferably, teeth 46 are integrally formed and coextensive withcylindrical wall 18. In this embodiment, an edge 54 is defined at firstend 20 of top section 14 and a flange 56 is disposed around theperiphery of wall 18 at a point set back from edge 54. Teeth 44 andnotches 48 are formed by flange 56 such that teeth 44 extend axiallyalong a length of wall 18. A portion of wall 18 extends beyond flange 56to define a lip 58.

In the foregoing embodiment, the outer diameter of cylindrical wall 18is substantially equal to, albeit slightly smaller than the innerdiameter of bottom 16 so that lip 58 can seat in the open end 32 ofcontainer 16. In such case, bottom 16 may include an o-ring 59 disposedwithin its interior to form a seal with lip 58. In any event, when lip58 is so seated, the alternating teeth 44 of flange 56 engage thealternating teeth 46 extending from edge 52. Preferably, the outerdiameter of flange 56 is substantially the same as the outer diameter ofwall 30 so that the interleaved teeth 44, 46 are flush with one another.

In another embodiment of the invention, a fastener system for case 12 iscomprised of groove 60 is formed in a portion of cap section 14 and agroove 62 is formed in a portion of container section 16. When capsection 14 and container section 16 are joined together, grooves 60 and62 align to form a peripherally extending groove around the periphery ofsaid case 12. A band fastener 64 is disposed to mount in saidperipherally extending groove, thereby securing cap section 14 andcontainer section 16 together. Preferably band fastener 64 is sized soas to fit in the peripherally extending groove such that the outerdiameter of fastener 64 is flush with outer surface 36 of wall 30.

Band fastener 64 is any type of fastener that is deployablesubstantially around the circumference of case 12 to secure the twosections together. Those skilled in the art will appreciate that such aband fastener may include, without limitation, a split ring, a snapring, a spiral retaining ring or an elastic band, such as an o-ring.

In one preferred embodiment, band fastener 64 is formed of metal andcase 12 is formed of plastic, such that the two components of unit 10have different expansion and contraction characteristics as unit 10 issubject to temperature changes. In the past, utilizing traditionalelongated-type metal fasteners such as screws or pins to secure plasticcomponents of a case such as is described herein could result in unduestress on the plastic components as the traditional fasteners expandedunder heat, thereby damaging the threads or bore in which the fastenerswere disposed. Such expansion could also result in unequal securingforces applied to a case. Moreover, repeated removal of the fastenersfor maintenance of a case often results in damage to the fasteners, thefastener receptacles or both. Finally, debris from deployment, such asmud, dirt, etc., can render such fasteners difficult to manipulate. Thegroove and split ring fastener configuration of the current inventionovercomes these problems. Since the split ring rides in the groove,there is some play in the ring. It can move within the groove withoutcausing damage. Further, as the split ring expands under a temperaturechange, an even securing force is applied around the periphery of theentire case. In any event, regardless of the particular type ofcircumferential band fastener utilized, the band fastener of theinvention has the capability of flexing under thermal expansion of thecylindrical case of the seismic unit much more so than more rigidscrews, pins or similar fasteners utilized in prior art seismic units.

While such a fastener system need not be incorporated with a case havinginterleaved teeth as described above, in one preferred embodiment, eachtooth 44, 46 includes a groove 60, 62, respectively, so that when teeth44, 46 are meshed together, the peripherally extending groove overlayssaid meshed teeth.

It will be appreciated that interleaved teeth and the band fasteningsystem described above are all desirable because they accomplish theirvarious purposes while at the same time permitting a substantial lengthof the sides of the case to remain smooth, without protrusions of anytype. This not only enhances coupling with the ground, but alsofacilitates deployment and retrieval of unit 10. The foregoingcylindrical unit 10 permits the unit to be easily placed in the ground,as opposed to traditional seismic units that are just commonly placed onthe surface of the ground. Those skilled in the art will appreciate thatunits placed in the ground not only have a better coupling with theearth, but are also less subject to physical force that may be placed onthem when simply deployed on the ground surface. In this same vein,noise, such as from wind or other energy sources, is further minimized.Preferably, the unit can be deployed in the field by simply boring ahole in the ground utilizing standard boring or coring equipment andinserting the cylindrical unit 10 into the hole.

Container section 16 preferably tapers along a portion of its length, asis shown at 65, from a first larger diameter, i.e., the diameter at thefirst end 20, to a second smaller diameter at the second end 22 ofcontainer section 16. During retrieval, the tapered section aids indecoupling unit 10 from the bore hole.

A spike 66 may also be provided adjacent end 40 to further facilitatecoupling of unit 10 with the ground.

One or more notches 68 may be provided in case 12 to facilitatehandling, manipulation, alignment, etc. of unit 10.

Preferably, cap section 14 and container section 16 join together toform an internal compartment 17 in which is disposed at least onegeophone, a clock for synchronization of unit 10, a power source, acontrol mechanism and a seismic data recorder, thereby forming aself-contained seismic data acquisition unit. In such a configuration,electronics may be mounted in both the cap section 14 and the containersection 16. Those skilled in the art will appreciate that by employinginterleaved teeth as described herein, the adjoining sections 14, 16 areprevented from twisting relative to one another, thereby potentiallydamaging internal wiring that may join the electronics mounted in thetwo sections.

In this same vein, a unique electrical contact system may be utilized inunit 10. In one preferred embodiment, unit 10 includes one or moreexternal electrical contacts 100 (see FIG. 3) deployed in case 12,thereby permitting external electrical contact with certain electricalcomponents within unit 10, for purposes such as recharging batteries,data extraction, quality control and the like. The electrical contactsare ruggedized in the sense that they are designed to eliminate damageto them from the harsh environments in which the units may be deployed.Moreover, the contacts 100 are physically decoupled from the internalcircuit board(s) of unit 10, thereby avoiding stress on the circuitboard from the varied expansion and contraction of the various physicalcomponents of unit 10, such as the plastic housing and the circuitboard.

At the heart of the electrical contact system is a “free floating”,electrically conductive pin 102, shown in FIG. 4. Pin 102 is elongatedand cylindrical in shape having a first end 104 and a second end 106.Pin 102 includes one or more o-ring grooves 108 along its length,preferably at least one of which is adjacent said first end 104.Adjacent the second end 106 of pin 102 is a c-clip groove 110 forreceipt of a c-clip (shown in FIG. 6). A flange 114 is defined on pin102 along a portion of its length between first end 104 and second end106. In the preferred embodiment, flange 114 tapers axially outward fromsaid first end to said second end to form a flared shoulder, as at 116.Finally, an aperture or bore 118 may be provided adjacent second end 106for attachment of an electrically conductive wire (not shown). Bore 118is shown as axially defined in pin 102 extending inward from second end106 towards first end 104.

Those skilled in the art will appreciate that c-clip groove 110 is justone of many possible fastener attachment structures that could beutilized to secure pin 102 as taught herein. Another non-limitingexample would be a radial bore passing through the end of pin 102 inwhich a pin or other fastener could be deployed. Likewise, second end106 could simply be threaded for receipt of an attachment nut.

Those skilled in the art will appreciate that aperture 118 is just oneof many possible wire attachment structures that could be provided as anattachment point for a wire to pin 102 as taught herein. Anothernon-limiting example would be a radial bore passing through the end ofpin 102 through which a wire could be passed. Notably, such anarrangement could also be utilized as a fastener attachment structure.

With reference to FIGS. 5 and 6, pin 102 is disposed to mount on asupport structure 120, such as a circuit board, carried within case 12.Specifically, support structure 120 includes an oversized through bore122 through which the second end 106 of pin 102 is disposed to passuntil flange 114 abuts upper surface 124 of support structure 120.Through bore 122 is preferably sized with an inner diameter large enoughto allow pin 102 to “wobble” or have free radial movement within throughbore 122. In other words, when pin 102 is co-axially aligned in throughbore 122, an annulus 123 is formed between the wall of through bore 122and pin 102.

Those skilled in the art will appreciate that the use of the term“oversized” refers to the inner diameter of through bore 122 relative tothe external diameter of the second end 106 of pin 102 within bore 122and simply means that the inner diameter of bore 122 is at least aslarge as the external diameter of second end 106 of pin 102.

As best seen in FIG. 4, when flange 114 abuts upper surface 124, aportion of pin 102, including c-clip groove 110, protrudes from throughbore 122, thereby permitting a fastener 112 to be utilized to secure pin102 to support structure 120. In the illustrated embodiment, fastener112 is a c-clip that mounts in c-clip groove 110 and can abut lowersurface 126 of support structure 120.

The first end 104 of pin 102 is disposed to seat within a pin housingstructure 128 provided in case 12. In one preferred embodiment, shown inFIG. 3, pin housing structure 128 is provided in cap section 14. In anyevent, pin housing structure 128 includes a through bore 130 having afirst end 132 and a second end 134 and disposed for receipt of first end104 of pin 102. In the preferred embodiment, through bore 130 includesan outwardly tapering portion 136 adjacent its second end 134. Theoutwardly tapering portion 136 is disposed to receive the flaredshoulder 114 of pin 102, thereby assisting pin 102 in orienting andaligning in pin housing structure 128. One or more o-rings 131 may becarried on pin 102 to sealably engage through bore 130, inhibitingmoisture or debris from entering internal compartment 17 of case 12. Asshown in FIG. 4, such an arrangement forms a ruggedized electricalcontact since the upper surface of pin 102 at 104 forms an exposedelectrical connection pad.

A flexible electrical wire 125 attached to aperture 118 forms aconductive path between pin 102 and electrical components of unit 10,such as the electrical contacts 127 of a printed circuit board. Sincepin 102 is physically disengaged from rigid attachment to a supportstructure such as a circuit board, various forces that may be placed onpin 102 are not transmitted to the circuit board on which pin 102 iscarried. For example, any unequal expansion or contraction of metal pin102 and plastic case 12, i.e., side-to-side movement, of case 12,resulting in forces on pin 102 will not jeopardize the more delicatecircuit board on which pin 102 is carried, but will be localized in pin102 which moves freely relative to the circuit board. Since theelectrical wire 125 is flexible, the end of the wire attached to pin 102can likewise move with pin 102.

Another embodiment of the electrical pin of the invention is shown inFIG. 7, wherein the flange 114 of pin 102 is replaced by an abutmentstructure 150. Those skilled in the art will appreciate that abutmentstructure 150 can take many configurations so long as some structure isprovided to prevent pin 102 from fully passing through bore 122. In theembodiment of FIG. 7, abutment structure 150 comprises a second c-clipgroove 110 for receipt of a c-clip 112.

Regarding the electronics of unit 10, it is also desirable to utilize acylindrical case 12 as described herein to improve vector fidelity. Theaccelerometer package, such as a geophone, is mounted along the majoraxis of case 12 so that the physical structure around the geophone issymmetrical. A seismic data acquisition case of a different shape,particularly those with walls that come together to form an edge orcorner, provide structure that can alter a signal path, therebydegrading vector fidelity and the quality of the seismic data recordedby the unit. Similarly, the unit utilizes an antennae positioned alongthe major axis of case 12, giving it a more uniform GPS sensitivity forlocation and timing purposes regardless of satellite location, therebyproviding a more uniform ground plane.

The foregoing describes a unique seismic data acquisition unit 10. Thecase is cylindrical in shape. This not only enhances vector fidelity,but also coupling with the ground and deployment of the unit. Thoseskilled in the art will appreciate that a better coupling will beachieved by “planting” units in the ground as opposed to simplydeploying the units on the surface of the ground. However, such plantingcan be time consuming because it creates the need to dig a hole and thenback fill the hole once a unit is positioned therein. The cylindricalcase permits a cylindrical hole of substantially the same diameter ofthe case to quickly be dug, utilizing devices commonly available fordigging cylindrical holes, such as augers, post hole tool or the like.Notably, such tools would not be overly useful for non-cylindrical casesbecause the additional labor of “planting” a unit would not beeliminated.

In any event, the case 12 is secured together utilizing acircumferential band fastener system that can be manipulated as neededto open or close case 12 much more quickly and easily than fasteners ofthe prior art. The fastener system also eliminates the need for externalflanges, lips or other structure projecting from case 12, therebypermitting sides of case 12 to remain smooth. Moreover, the systemminimizes transmission of damaging forces between case 12 and band 64under the unequal thermal expansion and contraction various componentsof the unit 10 experience during deployment.

In addition, case 12 utilizes interleaved fingers 44, 46 to preventtwisting or rotation of the cylindrical cap section 14 relative to thecylindrical container section 16, thereby protecting the variouselectrical components that may be mounted in these sections. The fingersare further disposed to join together to provide a smooth externalsurface for case 12, enhancing deployment and retrieval as well ascoupling with the earth.

Finally, unit 10 eliminates prior art socket or pin style electricalconnectors commonly used in seismic units by providing one or morefree-floating pins that form electrical “pads” that are easilyaccessible for electrical communication with the electronics of unit 10,but are physically decoupled from rigid attachment to the circuit boarsof the electronics so that expansion of the plastic case around pin 102will not cause stress on the circuit boards. Such pads are also easy toclean and easy to electrically engage.

The unit is also self-contained and wireless, requiring no wiringexternal to case 12 in order to operate during deployment.

While certain features and embodiments of the invention have beendescribed in detail herein, it will be readily understood that theinvention encompasses all modifications and enhancements within thescope and spirit of the following claims.

1.-25. (canceled)
 26. An electrical contact comprising: an elongated,electrically conductive, pin having a first end and a second end anddefined along an axis; an o-ring groove defined adjacent the first end;a fastener attachment structure defined adjacent the second end; ashoulder defined on said pin between said o-ring groove and saidfastener structure; and a wire attachment structure defined adjacent thesecond end.
 27. The electrical contact of claim 26, wherein saidshoulder tapers axially outward from said first end to said second endto form a flange.
 28. The electrical contact of claim 26, wherein saidfastener attachment structure is a c-clip groove.
 29. The electricalcontact of claim 26, wherein said fastener attachment is an aperturepassing radially through said pin.
 30. The electrical contact of claim26, wherein said wire attachment structure is a bore axially defined insaid pin at said second end.
 31. The electrical contact of claim 26,wherein said wire attachment structure is a bore radially defined insaid pin adjacent said second end.
 32. An electrical contact comprising:an elongated, electrically conductive, pin having a first end and asecond end and defined along an axis; an o-ring groove defined adjacentthe first end; a c-clip groove defined adjacent the second end; a flangedefined on said pin between said o-ring groove and said c-clip groove,wherein said flange tapers axially outward from said first end to saidsecond end to form a flared shoulder; and a bore axially defined in saidpin at said second end and extending inward from said second end towardssaid first end.
 33. An electrical contact system comprising: anelongated, electrically conductive, pin having a first end and a secondend and defined along an axis; an o-ring groove defined adjacent thefirst end; a c-clip groove defined adjacent the second end; a flangedefined on said pin between said o-ring groove and said c-clip groove,wherein said flange tapers axially outward from said first end to saidsecond end to form a flared shoulder; a bore axially defined in said pinat said second end and extending inward from said second end towardssaid first end; a circuit board with a first upper surface and a secondbottom surface and a aperture extending therethrough which aperture isdefined by an aperture wall, said pin mounted in said aperture so thatsaid flared shoulder abuts the first surface of said circuit board andsecond end of said pin extends through said circuit board aperture sothat the second end of said pin is spaced apart therein so as to form anannulus between said pin and said aperture wall, said circuit boardfurther including an electrical contact thereon; a c-clip mounted insaid c-clip groove adjacent said second surface of said circuit board,thereby securing said pin in said circuit board aperture; a flexibleelectrical wire attached at a first end to said bore axially defined insaid pin and at a second end to the electrical contact of said circuitboard; a pin housing structure, wherein said pin housing structurecomprises a wall with a through bore defined therein, said through borehaving a first end and a second end, wherein a portion of said throughbore tapers outwardly from said first end to said second end, whereinsaid circuit board is secured adjacent said pin housing structure sothat the first end of said pin extends into the through bore of the pinhousing structure from the second end so that the flared shoulder ofsaid pin is adjacent the outward taper portion of said through bore; andan o-ring mounted in said o-ring groove of said pin and sealablyengaging the through bore of said pin housing structure.
 34. Theelectrical contact system of claim 33, wherein said pin housingstructure comprises a case for a seismic data collection unit, said caseforming a sealed enclosure in which said support structure is mounted.35. An electrical contact system comprising: an elongated, electricallyconductive, pin having a first end and a second end and defined along anaxis; an o-ring groove defined adjacent the first end; a first fastenerattachment structure defined adjacent the second end; an abutmentstructure provided on said pin between said o-ring groove and saidfastener structure; and a wire attachment structure defined adjacent thesecond end; a support structure with a first upper surface and a secondbottom surface and an aperture extending therethrough which aperture isdefined by an aperture wall, said pin mounted in said aperture so thatsaid abutment structure abuts the first surface of said supportstructure and said second end of said pin extends through said supportstructure aperture so that the second end of said pin is spaced aparttherein from said aperture wall; a fastener attached to said firstfastener attachment structure so as to be adjacent said second surfaceof said support structure, thereby securing said pin to said supportstructure aperture; at least one electrical component; an electricalwire attached to said wire attachment structure at a first end and at asecond end to the electrical component; a pin housing structure, whereinsaid pin housing structure comprises a wall with a through bore definedtherein, said through bore having a first end and a second end, whereinsaid support structure is secured adjacent said pin housing structure sothat the first end of said pin extends into the through bore of the pinhousing structure from the second end; and an o-ring mounted in saido-ring groove of said pin and sealably engaging the through bore of saidpin housing structure.
 36. The electrical contact system of claim 35,wherein said support structure is a circuit board.
 37. The electricalcontact system of claim 36, wherein said electrical component comprisesan electrical contact on said circuit board.
 38. The electrical contactsystem of claim 35, wherein said aperture of the support structure iscircular and said pin is spaced apart therein so as to form an annulusbetween said pin and said aperture wall.
 39. The electrical contactsystem of claim 35, wherein said abutment structure is a flange.
 40. Theelectrical contact system of claim 39, wherein said flange tapersaxially outward from said first end to said second end to form a flaredshoulder.
 41. The electrical contact system of claim 35, wherein aportion of said through bore is sized to fit around said abutmentstructure.
 42. The electrical contact system of claim 40, wherein aportion of said through bore tapers outwardly from said first end tosaid second end so that the flared shoulder of said pin is adjacent theoutward taper portion of said through bore.
 43. The electrical contactsystem of claim 35, wherein said abutment structure comprises a secondfastener attachment structure and a fastener attached thereto.
 44. Theelectrical contact system of claim 43, wherein said first and secondattachment structures are c-clip grooves formed in said pin and saidfasteners are c-clips, each disposed in a respective c-clip groove.